1. Field of the Invention
The present invention related to integrated circuits and, more particularly, to a seal ring structure of an integrated circuit chip having both a digital circuit and an analog and/or RF circuit on one chip.
2. Description of the Prior Art
Advances in fabrication technology have enabled entire functional blocks, which previously had been implemented as plural chips on a circuit board, to be integrated onto a single IC. One particularly significant development is mixed-signal circuits, which combine analog circuitry and digital logic circuitry onto a single IC.
However, a major technical hurdle to implementing mixed-signal circuits has been the coupling of noise between different portions of the IC, for example, from the digital to the analog portions of the IC.
Ordinarily, an integrated circuit chip includes a seal ring used to protect it from moisture degradation or ionic contamination. Typically, the seal ring is made of a stack of metal and contact/via layers and is manufactured step by step as sequential depositions of insulators and metals in conjunction together with the fabrication of the integrated circuit elements.
It has been found that the noise, such as those come from a digital power signal line such as VDD or signal pad of a digital circuit, propagates through the seal ring and adversely affects the performance of the sensitive analog and/or RF circuit.